A rotary damper is conventionally known as a damper that is used for example in various opening and closing mechanisms to impart torque to the opening and closing action of an opening and closing member. As this kind of rotary damper, there is known a mechanism that uses a viscous fluid, such as oil.
In a rotary damper with a mechanism that uses this viscous fluid, the damper function by the imparting of torque is basically constant. Accordingly, it is suitably used for a configuration that brakes the opening and closing action of an opening and closing member or the like with a constant force. Also, as a rotary damper of a mechanism that uses this kind of viscous fluid, for example, there is known a damper that uses silicon oil as the viscous fluid. In this kind of rotary damper, in order to prevent oil leakage (fluid leakage), a sealing member such as an O-ring is provided (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2005-114154).
However, in a rotary damper that employs a viscous fluid such as the aforementioned silicon oil, since the viscosity of the viscous fluid depends on temperature, the damper function also changes with temperature. In particular, when the temperature rises to 40° C. or higher, that change becomes large. Accordingly, in the case of being applied to a configuration in which it is desired to brake with a constant force, that is, with a constant damper function, regardless of temperature, problems arise even in a rotary damper that uses this kind of viscous fluid.
Also, in a rotary damper that uses a viscous fluid, since a sealing member for preventing oil leakage (fluid leakage) is needed as mentioned above, the configuration becomes complicated. Also, since a step for filling the viscous fluid is required, the assemblability is poor, and the productivity is adversely affected.
Therefore, the inventors of the present application proposed a rotary damper that uses an annular ring member made of elastomer or flexible rubber and a sliding portion that slides along the circumferential direction thereof without using a viscous fluid, and so exhibits a constant damper function by the frictional force due to the sliding (refer to Japanese Unexamined Patent Application, First Publication No. 2007-154990).
However, even in the rotary damper disclosed in Japanese Unexamined Patent Application, First Publication No. 2007-154990, there are the following issues that need to be improved.
Although rotary dampers differ depending on their use, for example, in the case of being actuated when a lid or door is opened, a rotary damper with a high rotational speed dependency is often required. That is, when a lid or a door is opened, an inertia force and the like acts in the latter period compared with the initial period or middle period, and the opening speed increases. As a result, there is the possibility of an excessive load acting on the attachment portion of the lid or door, and defects occurring such as a loud noise being made as a result of impact. In the rotary damper disclosed in Japanese Unexamined Patent Application, First Publication No. 2007-154990, the rotational speed dependency is comparatively low, and so is insufficient for meeting the performance required in the applications described above.
Also, in relation to temperature dependency, in the rotary damper disclosed in Japanese Unexamined Patent Application, First Publication No. 2007-154990, the torque variation rate is small compared to a rotary damper that uses a viscous fluid from room temperature to about 40° C., and it exhibits a constant damper function. However, when the temperature becomes higher than 40° C., the torque variation rate becomes comparatively large.